Vat savitri Pooja is performed on the Jyeshtha Paurnima (Full Moon Day). On this occasion, the married women worship the Vata Vruksha (Banyan Tree – which is also the national Tree of India).
Some ladies cut a branch of Banyan Tree, bring it home and worship it. After the pooja is performed the ladies wrap a cotton thread around the Tree. However, it is not a good practice as it involves hurting the Tree.
Ladies are expected to observe 3 days fast starting on Jyestha Shuddha Trayodashi (13th day of bright half of Jyeshtha). However, if it is not possible to observe 3 days fast, at least fast on the on Vat Paurnima day is desired.
The scientific reason behind going to a Banyan Tree and worshiping it by married women is; the fluid coming out of the leaves of Banyan Tree helps curing uterus related problems, which help during pregnancy. The peel of Banyan Tree also helps curing body aches and increases the life expectancy. Hence it is advantageous for the newly married women to be in the vicinity of Banyan Tree on this day as much as possible.
Some ladies also tie swings to the Banyan Tree and play with their friends.
Jyeshtha Shuddha 15 (Paurnima)